The invention relates generally to signal analysis devices and, more specifically, to a method and apparatus for calibrating signal analysis devices and associated signal probes.
Oscilloscopes, frequency counters, digital multimeters, logic analyzers and the like typically receive input signals in various frequency bands through voltage attenuation probes or optical input probes. Users of such apparatus need to have confidence in the measurements they are making and that probes used to facilitate such measurements are working correctly.
Oscilloscopes, for example, typically provide a probe calibration output terminal that supplies a calibration signal. According to one common calibration method, a square wave signal from a calibration generator is applied to the probe, and the output signal waveform from the probe is observed with an oscilloscope. When the output signal waveform is a correct square-wave, the probe is determined to be calibrated. When the output signal waveform from the probe is not a correct square-wave, the probe calibration is adjusted while observing the waveform with the oscilloscope.
Unfortunately, typical probe calibration schemes suffer from several deficiencies, including: (1) an expectation that users are experts, as evidenced by a lack of user messages or user prompts explaining to users how to perform a calibration or what to look for during the calibration procedure; (2) the loss of previous instrument settings due to adjustments made to acquire and observe a probe calibration signal, thereby making it difficult for the user to return to a previous task; and (3) the lack of automatic adjustment of amplitude readouts in response to a determination of the attenuation factor of a particular probe.
These and other deficiencies of the prior art are addressed by the present invention of a method and apparatus for calibrating at least one signal probe associated with a test or measurement device. The invention advantageously allows rapid and accurate calibration, as well as the automatic return to a pre-calibration operating mode of the test or measurement device.
The subject invention is adapted, in one embodiment, to an oscilloscope such that a signal applied to a probe results in the storage of the operational parameters of the input channel in communication with the probe, the analysis of the calibration signal provided by the probe to the input channel, the adaptation of the calibration or operational parameters of the probe and, optionally, in response to this analysis, the restoration of the calibration or operational parameters, as modified. Calibration or operational parameters of the input channel supporting the probe may also be adapted.